The invention relates to novel thermoplastic block copolymers that can be produced by condensation polymerization and that consist of poly(meth)acrylate and polyamide segments, to their production, and to the use thereof. The inventive block copolymers exhibit a unique combination of the characteristics of poly(meth)acrylates (PMMA) and polyamides, can be used as modifying agents both in polyamide and in poly(meth)acrylates, and act as compatibility promoters in blends or are tailor-made adhesion promoters in multilayer systems such as multilayer polymer pipes.
Polyamides are among the most important technical thermoplastics, with diverse applications in a wide variety of fields. This versatility results from the fact that polyamides are modifiable in manifold ways, which makes it possible to produce tailor-made products. Copolymer formation, besides its utility for introducing reinforcing and filling agents, blending with other polymers, and adding various additives, is an important means of purposefully influencing the characteristics of polyamides. The linear block polymers that are known from the literature are primarily those containing segments based on polyethers, polyesters, polysiloxanes, polyimides and polycarbonates, besides the polyamide segment (J. Stehlicek, J. Horsky, J. Roda, A. Moucha in “Lactam based Polyamides” Vol. 2, R. Puffr, V. Kubanek, Ed., CRC Press, Boca Raton 1991, 20ff). But few examples can be found of the combination of polyamides and segments based on vinyl monomers. One exception is block copolymers consisting of polyamide 6 and polystyrol, poly(butadiene co-acrylic nitrile)(Colloid Polym. Sci. (1989), 267(1), 9-15), poly(styrol co-butadiene), polybutadiene and polyisobutylene.
Hitherto, block copolymers consisting of polyamide and poly(meth)acrylate segments have been obtainable from high-molecular (i.e. oligomeric) polyamides only by means of radical polymerization of macromolecular initiators. The synthesis of these initiators from polyamide pre-condensers, usually furnished with amino end groups, is carried out either by conversion with suitably functionalized low-molecular azo or peroxo initiators (Polymer Journal 31 (10), 864-871), or by nitrosation of a commercial polyamide and subsequent photochemical rearranging in the corresponding high-molecular diazoester (J. Polym. Sci., Polym. Chem. Ed. (1980), 18(6), 2011-20; J. Polym. Sci., Polym. Chem. Ed. (1982), 20(7), 1935-9). It is thus possible to produce AB, ABA or, by nitrosation, segmented multiblock copolymers by thermally or photochemically induced radical mass polymerization or solution polymerization.
With the photochemically or thermally induced decomposition of the diazoester, biradicals usually emerge, which give rise to branchings and cross-linkings. Many of the products are thus rubbery and insoluble. The formation of graft polymers is unavoidable owing to the high transfer rate. Furthermore, the characteristics of these copolymers are determined almost completely by the vinyl components. The yield of conversion with MMA (methylmethacrylate) is insufficient. Whereas a nearly total conversion occurs for the reaction pair of polyamide 6/acrylic nitrile (or vinyl acetate), the conversion is only 25% for MMA.
In the case of polyamide oligomers with azo end groups, only AB or ABA block copolymers are obtainable. The conversions must be carried out in solution. The initiator effectiveness is very low, so that inconsistent products are formed. Owing to the required reaction procedure, limitations in the concentration, segment length, and composition of the polyamide precondensate can be expected, because these parameters directly determine the dissolving behavior of the components and determine the solution viscosity of the reaction mixture.
The polycondensation of a polymethacrylate macromonomer with polyamide generating monomers for producing graft copolymers was described for the first time by Y. Yamashita in Polymer Bulletin 5 (361-366). The PMMA macromonomer was obtained by the radical polymerization of MMA in the presence of thio amber acid as the chain transfer agent. The generating of the polyamide backbone was accomplished by catalyzed polycondensation with aromatic diamines and aliphatic dicarboxylic acids in solution.
Besides this, Y. Chujo et al. describes the use of 2-mercaptoethanol and 2-aminoethane thiol as the chain transfer agent for functionalizing PMMA oligomers in J. Polym. Sci., Part A: Polymer Chemistry 27, 2007-14 (1989). The generated monofunctional PMMA oligomers are converted into the corresponding PMMA dicarboxylic acid by subsequent reaction with trimellitic acid anhydride. Macromonomers are thus available for the polycondensation. The resulting copolymers are graft copolymers with a polyamide main chain and PMMA side chains.
By preforming the PMMA macromers, it is possible to avoid the complications that arise in the radical polymerization; however, the building of the aforementioned polyamide chains must also be performed in solution. But the use of the a-bifunctional macromers only makes possible the synthesis of graft copolymers.
Thermoplastic polyamide blends consisting of polyamide 6 and anionically produced block polymers based on polyamide 6 are described in U.S. Pat. No. 4,501,861. The oligomeric diols used there, which include poly(alkylacrylate), must be converted on both ends of the chain with an acyl lactam unit, in order to make possible incorporation during the anionic polymerization of capro lactam.
The anionic ring opening is limited to lactams and requires a high purity of the utilized components, particularly absolute anhydrousness. The diols must also be fully refunctionalized; otherwise, break-off centers for the anionic polymerization will be created, which result in a high residual lactam content and a low polymerization grade. Reproducibility is therefore a primary problem of this process as well.